The present invention concerns method and apparatus for control of a steerable landing gear. More particularly, but not exclusively, this invention concerns a method of controlling the steering of a steerable landing gear on an aircraft with the aim of reducing undesirable vibration of the aircraft that might otherwise be caused. The invention also concerns a control apparatus for controlling the steering of a steerable landing gear on an aircraft for such a purpose, and also associated software. The invention also concerns an aircraft employing such a control method or apparatus.
When controlling the motion of an aircraft during taxiing operations on the ground, there may be circumstances in which vibrations are felt within the aircraft during certain manoeuvres. Vibration may be felt particularly when turning the aircraft by means of using a steerable landing gear. The inventors of the present invention have explored whether assisted, automatic, or semi-automatic control of the aircraft on the ground when turning might provide a means for reducing such vibration. There are various prior art documents concerning control systems for use when an aircraft is performing manoeuvres on the ground, including US 2014/0209739, U.S. Pat. No. 8,521,365, WO 2014/076485, WO 2014/076486, and those documents are mentioned and described in further detail below.
US 2014/0156113 describes a method of controlling the steering of a nose landing gear of an aircraft on the ground in which a steering angle position setpoint is set in dependence on the longitudinal speed and the yaw rate of the aircraft, those being characteristics of the movement of the aircraft, and without reliance on a measurement from a sensor for measuring the rotational position of the nose landing gear.
US 2012/0046834 describes a method of controlling the steering of a nose landing gear of an aircraft on the ground by means of utilising a closed-loop control system which controls to a yaw rate setpoint as compared to a measured yaw rate.
U.S. Pat. No. 4,482,961 describes a control system for assisting the control of the travel of an aircraft along a runway during landing, particularly under conditions of combined crosswind and low runway friction. Aircraft rudder control, nose landing gear steering control and differential braking are used to varying degrees depending on the phase of the landing operation (speed of the aircraft/weight on ground). U.S. Pat. No. 4,482,961 suggests seeking to limit the aircraft ground velocity slip angle to a range wherein an increase in ground velocity slip angle results in increased lateral corrective force on the aircraft (i.e. ensuring that the slip is maintained within a beneficial range on the slip-curve). To achieve this, the partial derivative of the aircraft lateral acceleration with respect to ground velocity slip angle is calculated and utilized by the control system. Such a partial derivative may be calculated by dividing the partial derivative of the aircraft lateral acceleration with respect to time by the partial derivative of the ground velocity slip angle with respect to time and this is suggested in US '961. In U.S. Pat. No. 4,482,961, there is described a steering controller that is arranged to issue a steering control signal that actuates the steering of the nose landing gear and that generates the steering control signal in dependence on a ground velocity slip angle and other control variables being either proportional to, or integrals of, parameters concerning aircraft velocity, the ground velocity slip angle, the ground roll course error signal (the difference between current direction of travel and the target direction of travel), aircraft yaw rate and aircraft yaw position. U.S. Pat. No. 4,482,961 is concerned with controlling the movement of the aircraft, at the aircraft-level, such that control of the nose landing gear is one part of an integrated control system.
None of the aforementioned prior art concern the problem of reducing vibration sustained by the aircraft when on the ground, however.
The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved apparatus and/or method for control of the motion of an aircraft during manoeuvres on the ground, such as taxiing. Alternatively or additionally, the present invention seeks to provide an improved apparatus and/or method for control of the steering of a steerable landing gear of an aircraft during manoeuvres on the ground, such as taxiing.